Interpretive Summary: Tephritid fruit flies are serious economic pests worldwide. The larval stages feed within host fruits, making infestation difficult to detect. Fruit imported into the U.S. is currently checked for infestation by cutting open a small sample of fruit and looking for fly larvae. The efficacy of this inspection procedure is questionable, so there is a need for more sensitive screening methods. USDA-ARS scientists (Subtropical Horticulture Research Station, Miami, FL) in conjunction with USDA-APHIS-PPQ (Miami, FL) conducted research to evaluate gas chromatography (GC) as a method for improved detection of hidden infestation. Grapefruits infested with larvae of the Caribbean fruit fly were examined to determine if infested fruit emitted chemicals distinct from those of healthy fruit. GC analysis indicated there were volatile chemicals indicative of citrus fruit injury (limonene and ocimene) and others associated with larval infestation (hexyl butanoate and an unknown compound yet to be identified). These “signature chemicals” were also detectable with a portable ultra-fast GC analyzer. Further studies will investigate the potential application of these results for development of a rapid screening protocol for detection of infested fruit at U.S. ports of entry.

Technical Abstract:
Tephritid fruit flies are serious economic pests worldwide. As larvae, they feed and develop within the pulp of host fruits, making infestation difficult to detect by visual inspection. At U.S. ports of entry, incoming produce shipments are checked for infestation by manually cutting open a small sample of fruit and searching for tephritid larvae. Consequently, there is a need for more sensitive, high-throughput screening methods. This study evaluated gas chromatography (GC) as a potential technology for improved detection of hidden infestation. Grapefruits (Citrus x paradisi Macfad.) infested with immature stages of the Caribbean fruit fly Anastrepha suspensa (Loew) (Diptera: Tephritidae) were examined to determine if infested fruit emitted a chemical profile distinct from that of non-infested fruit. Peaks identified by GC analysis were grouped into three classes. Chemicals detected in similar quantities in all samples, or slightly elevated in infested samples, were regarded as non-diagnostic background volatiles. Chemicals highly elevated after oviposition, during the last instar exit stage, and in experimentally-pierced fruit were interpreted to be indicators of citrus peel injury, and included D-limonene and ß-ocimene. Chemicals elevated exclusively in the larval infestation stages were considered indicators of feeding damage and potentially diagnostic of infestation, and included hexyl butanoate and an unidentified compound. The peaks associated with injury and feeding were also detectable with a portable ultra-fast GC analyzer that required less than 80 sec per sample. Further studies will investigate the potential application of these results for development of a rapid, non-destructive screening method for detection of tephritid infestation.